Secondary Battery Resistance Factor Determination for Safe Charging
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Solution Overview
Problem
Current methods for estimating charge power in secondary batteries, such as HPPC, do not consider state of charge and current design limits, leading to potential overcharging and safety risks, especially in lithium batteries.
Innovation Solution
A method and apparatus for determining a resistance factor of a secondary battery by measuring initial and final voltage data at varying charging currents and temperatures, creating a look-up table to estimate charge power within safe limits, preventing excessive voltage or current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If HPPC method is used to estimate charge power considering only voltage design limits, then the power calculation is simple, but the estimation accuracy deteriorates and safety risks increase due to ignoring state of charge and current design limits
Solution Approach 1:
The patent changes the parameters used in power estimation from simple voltage-based HPPC method to a comprehensive approach incorporating state of charge (SOC), temperature, and current design limits. This is achieved by creating resistance factor look-up tables that are functions of multiple parameters (SOC and temperature) rather than using a constant resistance value, thereby improving estimation reliability while maintaining computational feasibility through pre-computed tables.
Solution Approach 2:
The patent performs preliminary experimental characterization to build resistance factor look-up tables before actual power estimation operations. These tables are pre-computed based on extensive testing across different SOC levels and temperatures, allowing the system to quickly retrieve accurate resistance factors during operation without performing complex real-time calculations, thus resolving the contradiction between accuracy and complexity.
2Productivity
If maximum charging current is determined without considering charge upper limit conditions, then the charge power is maximized, but the battery may be overcharged causing safety hazards
Solution Approach 1:
The patent implements a feedback mechanism where the estimated charge power is continuously monitored and compared against charge upper limit conditions (maximum voltage, current, and state of charge). The system adjusts the actual charging current based on this feedback to ensure it does not exceed safe operating limits, thereby preventing overcharging while maximizing charging speed within safety boundaries.
Solution Approach 2:
The patent makes the charging system dynamic by adjusting the maximum allowable charging current based on real-time battery state (SOC and temperature) rather than using a fixed current value. The resistance factor look-up tables enable the system to dynamically determine appropriate current limits for different operating conditions, optimizing charging speed while preventing harmful overcharging effects.
3Device complexity
If resistance factor is determined without considering temperature and state of charge variations, then the measurement process is simple, but the resistance determination accuracy deteriorates
Solution Approach 1:
The patent segments the resistance factor determination into discrete SOC levels and temperature ranges, creating a multi-dimensional look-up table structure. Instead of attempting to model continuous variations mathematically, the system divides the operating space into discrete segments and pre-determines resistance factors for each segment through experimentation, simplifying the measurement process while maintaining high precision through fine-grained segmentation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables reliable estimation of charge power within safety margins, preventing overcharging and ensuring safe battery operation by accurately determining resistance factors based on state of charge and temperature.
Implementation Method 1
an application of a high-performance secondary battery requires estimating a charge power corresponding to a state of charge (SOC) of the secondary battery
Implementation Method 2
HPPC models the voltage of a secondary battery simply by Equation 1 below. Here, OCV(z) is the open circuit voltage (OCV) of the secondary battery, which corresponds to the state of charge of the secondary battery, and R is a constant that represents the resistance of the secondary battery
Data Source
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AI summary
A resistance factor determining method of a secondary battery according to the present disclosure determines, when the secondary battery has a certain temperature and state of charge, a primary differential value regarding a charge initial I-V profile calculated from a current value at a point of intersection at which a charge final I-V profile according to changes in magnitude of the charging current meets a boundary line set to a charge upper limit as the resistance factor corresponding to the temperature and state of charge. Further, a charge power estimating apparatus and method according to the present disclosure estimates a charge power corresponding to the temperature and state of charge of the secondary battery while the secondary battery is being charged using the resistance factor pre-defined according to the state of charge and temperature of the secondary battery.